Heat 3 tablespoons olive oil in a large pan over medium-high heat. The corned beef cubes and brown on all sides, about 2 minutes each side, 8 minutes total. Work in batches if needed, keeping the meat in a single layer in the pan. Transfer to slow cooker.

Add the potatoes, carrot and butternut squash to the slow cooker. Add beef stock, Guinness, brown sugar, thyme and pickling spices to the slow cooker. Stir to combine. Cover and cook for 3 to 4 hours on high, or 6 to 7 hours on low. Potatoes should be fork tender.

In a medium sized bowl combine 6 tablespoons flour with 3/4 cups of the hot stew liquid, whisk to combine. Pour into slow cooker, stir to combine. Add the corn kernels. Cover and cook on high for 30 minutes. Stew liquid should thicken slightly. Stir and taste liquid, season with more salt and pepper as desired.